This invention relates to a device for microbiological purposes which includes a nutrient card and a film made from a synthetic resin dispersion lying thereabove, the nutrient card and the dispersion film being combined to form a test unit.
The investigation of certain body fluids for the presence of micro-organisms, such as the detection of bacteria and fungi in urine, provides the physician, microbiologist and the like with valuable indications for the diagnosis of particular diseases. Consequently, numerous test means have been developed in recent years for the detection of bacteria and fungi.
However, detection means of this type are also used for the investigation of pharmaceuticals, foodstuffs, water, swimming pools and the like where certain kinds of microorganisms are harmful or can constitute a danger to health.
The known processes of culturing and detecting microorganisms depend upon the fact that various selected nutrients and possibly selectively inhibiting agents are worked up with agar-agar to give a nutrient medium. Although nutrient media are important for special problems, they are disadvantageous for routine operations, especially when cost-saving and comparatively large numbers of samples are to be investigated. The nutrient media must be prepared by the user in a relatively laborious manner from a dry powder. Nutrient media ready for use are also commercially available in swollen form. However, nutrient agar media which are ready for use readily dry out and can then no longer be reversibly moistened, which means that they must be packed in moisture-proof packings which, in addition, take up a large volume.
More recently, especially for the investigation of foodstuffs and water, microbiological detection processes have been described in which nutrient cards are covered with membrane filters. For this purpose, the liquid to be investigated is filtered through a membrane filter, the membrane filter is laid upon a nutrient card moistened with sterile water or upon a filter card impregnated with sterile nutrient solution and this unit then cultured in a Petri dish. The micro-organisms retained on the membrane filter grow during the incubation period and become visible as colonies.
This process is only practicable when micro-organisms are to be detected in very small concentrations and, therefore, must be enriched before detection by means of incubation. The membrane filters and nutrient cards are provided loose and, because of the brittleness of the membrane material, require especially careful handling. An improvement is provided by combining the membrane filter and the nutrient card into a single unit in a special frame (see German Pat. No. 2,115,674). This process admittedly simplifies handling but the production of the unit comprising the membrane filter and the nutrient card in a special frame is laborious and expensive.
The described filter processes are not suitable for medical diagnostic problems since a concentration of the micro organisms on the surface of the filter is not necessary and, indeed, because of the necessity of distinguishing high micro-organism counts, preferably in the range of from 10.sup.3 to 10.sup.8 micro-organisms per ml. of body fluid, is of great disadvantage.
Furthermore, processes are known in which a micro-porous membrane is produced on a nutrient card in such a manner that the membrane material partly penetrates into the card (see German Pat. No. 2,320,946). This process suffers from the disadvantage that the surface of the membrane has the same roughness or unevenness as that of the nutrient card. In the case of such a test, because of the unevenness of the surface, the micro-organisms are, without additional means, not visible at all or very poorly visible after the incubation. They must be rendered visible by coloring with dyestuffs. Therefore, the micro-organisms appear in a completely different manner to the viewer than in the case of the well-known detection processes on agar-agar. A visual differentiation of the species is not possible. The colonies, which penetrate more or less into the nutrient card, cannot be separately used for inoculation. However, such an inoculation is absolutely essential for a differentiation of micro-organisms and for an investigation of resistance behavior.
Another process is known which is essentially a further development of the above-described process, it having the object of overcoming the disadvantages of this process. This test, which is described in German Pat. No. 2,320,943, is improved in that, instead of the membrane layer or above the membrane layer, there is applied a gel layer, the gel layer and the nutrient card passing over into one another. It is thereby preferable also to incorporate nutrients into the gel layer. As is known from experience, such gel layers cannot be applied to paper surfaces with the same uniformity and smoothness as is possible in the case of swollen agar layers. Therefore, this process suffers from disadvantages which are similar to those possessed by the process according to German Pat. No. 2,320,946.